Project Summary/Abstract: Histoplasma capsulatum is a ubiquitous, thermally dimorphic fungus that causes disease worldwide, with an estimated 500,000 new infections per year in the United States and 15.4 cases per 1000 person years in Central and South America. There has been a marked increase in cases of disseminated histoplasmosis with the spread of HIV/AIDS and increasing exposure to potent immunosuppressive therapies. In Histoplasma-endemic areas, histoplasmosis is the first manifestation of HIV infection in 50-75% of patients and it is one of the leading causes of hospitalization and death in these individuals. A critical barrier to reducing morbidity and mortality in patients with histoplasmosis is the lack of diagnostic tools that identify histoplasmosis early and rapidly, and distinguish it from other common infections that present with a similar clinical syndrome, such as tuberculosis (TB). Existing diagnostic tests for histoplasmosis are insensitive, slow to yield diagnostic information, or require invasive procedures, specialized expertise, or laboratory facilities, making real-time clinical decision-making challenging. Once histoplasmosis is diagnosed, it is often challenging to assess the response to antifungal therapy due to slow resolution of clinical symptoms and abnormal laboratory and imaging findings. We propose a novel approach to the diagnosis of histoplasmosis based on detection of Histoplasma capsulatum volatile metabolites in the breath. We will test the hypotheses that patients with histoplasmosis have distinct breath metabolites that can be harnessed to differentiate patients with and without histoplasmosis rapidly and kinetics of these metabolites can be used to predict responses to antifungal therapy, by (1) identifying the set of breath volatile metabolites that distinguishes patients with histoplasmosis from patients with other histoplasmosis-like clinical syndromes, including TB, using laboratory-based analytical chemistry methods and, in parallel, rapid bedside gas chromatography-differential mobility spectrometry, and (2) examining the relationship between breath Histoplasma metabolite kinetics with antifungal therapy and ultimate clinical outcome. Successful completion of these aims would allow rapid, bedside identification of histoplasmosis and real time surveillance of the treatment response, reducing diagnostic delays, guiding antifungal treatment decisions, and improving clinical outcomes in patients with this common, life- threatening infection.